Single-monomer method synthesis

Polystyrene is the name of a homopolymer made from the single monomer styrene. When the name of a monomer comprises two or more words, the name should be enclosed in parentheses, as in poly(methyl methacrylate) or poly(4-bromostyrene) to identify the monomer more clearly. This method can result in several names for a given polymer thus, poly(ethylene glycol) , poly(ethylene oxide) and poly(oxirane) describe the same polymer. Sometimes, the name of a hypothetical monomer is used, as in poly(vinyl alcohol) Even though a name like polyethylene covers a multitude of materials, the system does provide understandable names when a single monomer is involved in the synthesis of a single polymer. When one monomer can yield more than one polymer, e.g. 1,3-butadiene or acrolein, some sort of structural notation must be used to identify the product, and one is not far from a formal structure-based name. 

Scheme 30.8 Hyperbranched polyphenylene synthesis by the single-monomer polycondensation method.

The repeating unit concept always refers to the structure of the macromolecular chain. The concept of the monomeric unit (or mer, also known as the base unit or monomeric base unit), on the other hand, is based on the polymerization process. It refers to the largest constitutional unit contributed by a single monomer during a polymerization process. Consequently, the constitutional repeating unit may, according to the structure or method of synthesis of the macromolecule, be the same size as or smaller or larger than the monomer unit (see Table 1-1). 

One of the early and well-documented methods for producing poly-arylethersulfones involves use of an electrophilic Friedel-Crafts polymerization process. First applied to PES, this synthesis route involved reacting bis(4-chlorosulfonylphenyl)ether in a 1 1 molar ratio with diphenylether [5—7]. Alternatively, a single-monomer Friedel-Crafts synthesis can be employed starting with 4-chlorosulfonyldiphenyl ether as the sole monomer. The Friedel-Crafts route to the production of sulfone polymers was used briefly on a commercial basis in the 1960s but was quickly abandoned due to a number of limitations. In addition to being operationally complex, this sjmthesis route yields polymers that are not always linear or para-linked. 

In this chapter we describe a new method of copolymer synthesis which is analogous to the method of isomerization polymerization, in that a copolymer is prepared from a single monomer The method is repeating unit isomerization, which we define as a polymerization followed by intramolecular rearrangement of the polymer repeating unit to a thermod3mamically more favorable structure (Eqn 4) ... 

The Merriheld method of peptide synthesis is deceptively simple. As shown in the diagram below, it begins with some means of solid support for the synthesis, resin beads in Merriheld s original work, to which is attached a single molecule that can serve as the basis (the monomer) for a far more complex molecule. In Merriheld s original research, the molecule attached to the resin head was an amino acid molecule. 

When a library is deconvoluted via an iterative method, both time and monomers are used in excess for synthesis during iteration rounds. Moreover, the iterative process ends with a single structure which may not be the most active compound of the library (see previous chapters) and the deconvolution of additional positives, when it is possible, considerably lengthens the structure determination process. 

Direct structure determination methods, where positives are characterized directly via off-bead or on-bead identification of their chemical structure, will be described in detail in this section. Indirect methods that determine the structure of positives from the library architecture will be covered later they use either deconvolutive methods (Section 7.3), where the iterative synthesis of library pools with decreasing complexity via sequential determination of the best monomers leads to the identification of a positive structure, or encoding methods (Section 7.4), where, during the library synthesis, the structure of each component is coupled to a tag that can be read from a single bead after the library screening. 

The combined (two-stage) methods use the copolymerizatton of the main monomer containii the labeling amount of the comonomer (bearing a reactive group) with sub quent modification of the units of the main monomer or the comonomer. It is desirable to apply these methods when the single-stage synthesis of a polymer with LM is impossible for some reasons or very complicated or when it is necessary to introduce LM with different dynamic or optical parameters into the samples of one polymer. 

Our research interest in this field is based on the perception that these dendritic polymers could be useful as polymer-rheology control agents as well as spherical, multifunctional macromonomers. Hyperbranched polymers, which were not only thermally and chemically robust under the conditions used, but also could be economically obtained, were created to evaluate these concepts. The latter requirement led us to pursue the one-step polymerization of AB -type monomers. We will review mostly the synthesis of aromatic polymers with stable chemical linkages prepared by the single-step direct method, and we will briefly compare them with polymers made by more controlled multistep syntheses. 

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